1. Field of the Invention
The invention relates to optical communication equipment and, more specifically, to micro-electromechanical devices for use in such equipment.
2. Description of the Related Art
Optical communication equipment may employ micro-electromechanical systems (MEMS). A representative MEMS device may have an array of micro-machined mirrors, each mirror individually movable in response to an electrical signal. Such an array may be employed as an element of a wavelength-selective switch. In operation, at least one mirror in the array receives a beam of light. The beam is reflected from the mirror and can be controllably redirected to a different location (e.g., a selected output port) by controlling the rotation angle of the mirror.
One problem with prior-art MEMS devices is related to manufacturing such devices. During fabrication, two pieces, e.g., wafers, are used to form the MEMS device, which pieces must be accurately aligned to properly position the actuating electrodes with respect to the corresponding mirror. Such alignment may be difficult to achieve for relatively small mirrors and/or mirror arrays having a relatively large number of mirrors.
Another problem with prior-art MEMS devices is referred to as “snap-down.” More specifically, when the voltage applied to an actuating electrode in such device exceeds a critical (snap-down) value, the tilt angle of the mirror increases rapidly and uncontrollably. This behavior may cause a collision of the mirror against the electrode and/or wafer, damaging the mirror and rendering the MEMS device inoperable.